Production of acrylonitrile



March 6, 1945. H. A. DUTCHER 2,370,849

E PRODUCTION-OF ARYLONITRILE Filed Dec. 6, 1945 SEPARATI NG MEANSACRYLONITRILE lo* INVENTOR H. A DU TCH ER ATI' NE the heat requirementsof the Fatented Mar. 6, 1945 2,370,849 PRODUCTION OF ACRYLONITRILEDelaware trams A. patcher, Bartlesville, Okla., Phillips PetroleumCompany, a corporation of assignor to Application December 6, 1943,Serial No. 513,095

4 Claims.

This invention relates to the production of acrylonitrile from gaseouspetroleum hydrocarbons and ammonia. More specifically, it relates to thepyrolysis of hydrocarbons such as methane or ethane in the presence ofammonia. and to the catalytic treatment of the pyrolysis eilluents toform acrylonitrile.

Acrylonitrile (vinyl cyanide), CHz=CH-CN, is an important ingredient inthe manufacture of certain types of synthetic rubber, and it has othervaluable chemical uses as well. None of the methods hitherto proposedfor its manufacture are entirely suitable for large scale commercialproduction, as they require materials which are relatively expensive andin some instances difficult and dangerous to handle.

It is an object of my invention to provide a continuous process for themanufacture of acrylonitrile from petroleum nia.

Another object of my invention is to provide a process in whichacrylonitrile is formed by catalytic treatment of the eiuents from ahydrocarbon pyrolysis carried out in the presence of ammonia.v

A further object is to provide a process in which the production ofhydrogen cyanide and acetylene by pyrolysis of petroleum hydrocarbons'with ammonia is combined in a novel'and advantageous manner with thecatalytic reaction of hydrogen cyanide and acetylene to formacrylonitrile.

Still another object is to prevent polymerization of hydrogen cyanideand acetylene during the catalytic process.

Another object is to provide a process in which catalytic step aresupplied by the heat contained in the pyrolysis eiiiuents.

I have now found that acrylonitrile may be produced in a highly improvedmanner by pyrolyzing a mixture of hydrocarbon and ammonia to form aneilluent containing hydrogen cyanide and acetylene, and subjecting theetiluent directly to catalytic treatment at a lower temperature, therebycausing the hydrogen cyanide and acetylene to combine to formacrylonitrile.

More specifically, in accordance with the invention, acrylonitrile isformed from low molecular weight hydrocarbons, e. g. methane or naturalgas, and ammonia, by a two-stage process in which the hydrocarbons andammonia are subjected to pyrolysis at temperatures of from 1000 to 1500C. and sub-atmospheric pressure, followed by a catalytic treatment ofthe eilluents at a temperature of 400 to 500 C. and atmospheric orhigher pressure.

The hydrocarbon used in the feed to the pyrolysis step may be anyhydrocarbon which yields acetylene upon pyrolysis. The hydrocarbon isusually a lower aliphatic hydrocarbon up to and hydrocarbons and ammotheeilluents The pyrolysis may be carried out in any convenient manner, thepreferred conditions of operation being the following: The hydrocarbonfeed should contain predominantly methane and/or ethane; the proportionof ammonia added may be varied over rather wide limits but the volumeratio of hydrocarbon to ammonia in the feed is usually between 10:1 and5:1; the reactant gases should be substantially free of oxygen; thetemperature should be at least 1000 C. and is preferably in the range1,300 to 1500 C. or even higher; the pressure is maintained atsub-atmospheric and preferably below 200 mm. of mercury; the contacttime should be less than 0.10 second and is preferably 0.05 second oreven less; are quickly cooled to a temperature in the range 40G-500 C.

Theheating may be done in non-porous refractory tubes contained in anelectric furnace or oven, or the tubes may be heated by hot gases.

The catalytic treatment ci. the eiiiuents from the pyrolysis step iscarried out at the temperature to which the gases are cooled immediatelyafter leaving the furnace, i. e. 40G-500 C. Thus, a major portion of theheat required in the catalyst chamber is supplied by the gasesthemselves and preheating of the feed to the catalyst chamber is notrequired. In effect, a double use is made of a'portion of the heatenergy supplied for the pyrolysis reaction. x

The feature of leading the pyrolysis eilluents directly into thecatalyst chamber (after cooling to the proper temperature) results inanother important advantage. The reaction to be carried out in thissecond step of the process is. of course, the direct combination ofacetylene according to the following equation:

It would :be expected. on the basis of chemical theory. that a maximumyield of acrylonitrile would be obtained froma reactant mixturecontaining only hydrogen cyanide and acetylene, and that any inertdiluent gases present (such as the hydrogen, methane, and nitrogenresulting from my pyrolysis reaction) would seriously lower the yield ofacrylonitrile obtained. I have found,

however, that such is not the case. Presumablyv hydrogen cyanide withyield of acrylonitrile is much improved. In other words, the increase inyield by the prevention of the several types of polymerization reactionsmore than compensates for any slight decrease in yield due to thediluent eiect upon the single desired reaction.

Still another advantage of my process results from the fact that theeiliuents from the pyrolysis step are used as the feed to the catalystchamber. In prior art processes for making acrylonitrile from hydrogencyanide and acetylene these materials are supplied separately to thereaction zone, thus necessitating storage and handling of poisonoushydrogen cyanide and explosive acetylene. In my process all dangersattendant to the handling of these materials are eliminated by usingthem in the second step of the 'process as fast as they are formed inthe rst.

The catalytic combination of hydrogen'cyanide and acetylene may becarried out in any conventional catalyst chamber in which gaseousreactants may be contacted with solid catalysts at temperatures withinthe specified range, i. e. 400-500" C. Preferred catalysts are thecyanides of the alkali and alkaline earth metals, particularly sodiumcyanide. They may be supported on porous materials such as silica gel,alumina, bauxite, and

the like. The contact time may vary over rather wide limits, dependingupon the composition of the pyrolysis effluent stream and upon thecatalyst temperature, but is generally in the range 0.5 to 2 seconds.Unchanged hydrogen cyanide and/or acetylene may, of course, be recoveredfrom the final products by known methods and recycled to the catalystchamber. Any tendency of either reactant to build up in this part of theprocess may be compensated for by varying the proportion of ammoniaintroduced into the pyrolysis reaction. Reducing the proportion ofammonia, for example, results in an excess of acetylene over hydrogencyanide in the pyrolysis eiiiuents, while an increase in the proportionof ammonia in the feed effects the reverse result. The relativeproportions of hydrocarbon and ammonia in the feed to the pyrolysis stepmay be such that the pyrolysis effluent contains approximately equimolaramounts of hydrogen cyanide and acetylene. A

The products leaving the catalyst chamber contain, besidesacrylonitrile, hydrogen, methane,

cooled eiuents pass from compressor I into catalyst chamber B.

The eiliuents from catalyst chamber 6 are quenched with water inquencher 1, from which they are passed to separating means 8. Hereacrylonitrile is recovered in conventional manner for example byfractional distillation, the acrylonitrile being removed via line 0.Light gases such as hydrogen and nitrogen are removed from the top ofquencher 1 through line 9.

Example Ammonia and natural gas in the ratio 1:9 by volume weresubjected to pyrolysis at 1500 C. and 100 mm. of mercury pressure. Therate of iiow was adjusted so as to give a contact time of 0.05 second.The eiiiuents were quickly cooled to 450 C. and passed over solid sodiumcyanide at a pressure slightly above atmospheric and with a contact timeof 1.5 seconds. The products were quenched with water and theacrylonitrile recovered by fractional distillation.

I claim:

l. The process for the production of acrylonitrile which comprisesadmixing a, low-boiling parafn hydrocarbon having one to two carbonatoms per molecule with ammonia in a gas volu me ratio within the rangeof ve to ten volumes of said hydrocarbon per volume of ammonia,subjecting said mixture to pyrolysis under conditions effecting theformation of hydrogen cyanide and acetylene, and passing the totaleiiluent of said pyrolysis into contact with the cyanide of an alkalimetal as catalyst under conditions eiecting the conversion of hydrogencyanide and acetylene to acrylonitrile.

2. The process for the production of acrylonitrile which comprisesadmixing a low-boiling hydrocarbon having one to `two carbon atoms per40 molecule with ammonia in a gas Volume ratio nitrogen, and perhapsunchanged hydrogen cy anide or acetylene. This eiiluent is cooled downto a. suitable temperature below the boiling point of acrylonitrile, forexample to room temperature.

It is preferred to cool these gases by a direct water quench as` theyleave the catalyst zone. Separation and recovery of the acrylonitrileand other components is then readily accomplished in con.

ventional manner.

I n the drawing a preferred embodiment of my process is illustrated indiagrammatic form. A preheated gaseous mixture of hydrocarbon andammonia is introduced through line I into pyrolysis unit 2. This mayconsist of a plurality of nonporous refractory tubes of small diameter(e. g. 10 mm.) heated to a temperature of 1500 C. by means of hot gases.The effluents pass through line 3 to cooler 4 where the temperature isreduced to about 450 C., and thence to compressor 5. By

' means of this compressor the pressure in pyrolysis chamber 2 ismaintained below 200 mm. of mercury while that in the catalyst chamber 6is slightly above atmospheric. Suitable valves (not shown) are of courseemployed in conjunction with this control of pressure. The compressedwithin the range of iive to `ten volumes of said hydrocarbon per volumeof ammonia, subjecting said mixture to pyrolysis at a temperature withinthe range of 1000 to 1500 C. under conditions eiecting formation ofhydrogen cyanide and acctylene, cooling the total eiiluent of saidpyrolysis to a temperature within the range of 400 to 500 C., andpassing the total eiiluent at said temperature into contact with thecyanide oi an alkali metal as catalyst under conditions effecting theconversion of hydrogen cyanide and acetylene in said effluent toacrylonitrile.

3. The process of claim 2 in which the paraiiin hydrocarbon compriseschiefly methane and the catalyst is sodium cyanide.

4. The process for the production of acrylonitrile which comprisesadmixing methane with ammonia in a gas volume ratio within the range ofve to ten volumes of methane per volume of ammonia, subjecting saidmixture to pyrolysis at a temperature within the range of 1300 to 1500C. and at a pressure within the range of to 200 mm. of mercury for aperiod of time within the range of 0.05 to 0.10 seconds eiectingformation of hydrogen cyanide and acetylene, cooling the total effluentof said pyrolysis to a temperature within the range of 400 to 500 C.,and passing the total eiiiuent at said temperature directly into contactwith a sodium cyanide catalyst at substantially atmospheric pressure fora period of time within the range of 0.5 to 2 seconds eiectingconversion of hydrogen cyanide and acetylene in said eiuent toacrylonitrile.

HARRIS A. DUTCHER.

CERTIFICATE oF. coRREcTIoN.

Patent No. 2,570,819. March 6, 19u15.

.HARRIS A. DUTCHER.`

It is hereby certified that error appears in the iprinted specification'of the ahove numbered patent requiring correction as follows: Page 2,second eo luinn, line 58, claim 2, after "low-boiling" insert-I-'paraf'fin-m; and

that thev said Letters Patent should be read with this correctiontherein that the same may conform to the record; of' the case in thePatent Office.

' Signed and sealed this 12th day of`June, A. .D,. 1914.5.

Leslie Frazer (Seal) Acting ommi'ssioner Vof Patents,

